Petroleum naphthalene manufacture



July 6, 1965 o. c. EUBANK PETROLEUM NAPHTHALENE MANUFACTURE 2 Sheets-Sheet 1 Filed Aug. ll, 1961 INVENTOR. 0564/? c. Edam/K July 6, 1965 o. c. EUBANK 3,193,593

PETROLEUM NAPHTHALENE MANUFACTURE Filed Aug. ll. 1961 2 Sheets-Sheet 2 United States Patent O M 3,193,593 PETRGLEUM NAPHTHALENE MANUFACTURE Oscar C. Eubank, Long Beach, Calif., assigner to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Aug. 11, 1951, Ser. No. 130,827 12 Claims. (Cl. 260-672) This invention relates to the manufacture of naphthalene from source materials of petroleum origin, and in particular concerns an improved process for the production of naphthalene by the catalytic or thermal dealkylation of alkyl-substituted naphthalenes obtained from various petroleum refining operations.

The expanding use of naphthalene for the production of dicarboxylic acids useful in manufacturing synthetic resins and fibers has created considerable interest in the manufacture of napthalene from petroleum hydrocarbons. It is well known that certain hydrocarbon fractions obtained in various petroleum refining operations, e. g., cracking and reforming, contain considerable quantities of alkylnapthalenes which can be thermally or catalytically dealkylated to form free napthalene. As such processes are conventionally carried out, a feedstock consisting of a reformate or cycle oil fraction boiling above about 430 F. and comprising alkylnaphthalenes and such nonnaphthalenic materials as alkylbenzenes, alkyltetralins, alkylindanes, etc., is subjected to dealkylating conditions to obtain an efliuent p-roduct which, after separation of normally gaseous materials such as hydrogen and low molecular weight hydrocarbons, is fractionally distilled to obtain: (l) a light gasoline fraction, (2) a naphthalene fraction, and (3) a heavy fraction comprising unreacted alkylnaphthalenes which, after the removal of heavy ends and polymers, is recycled to the reaction zone. According to one mode of operation, the naphthalene fraction is taken over a relatively wide boiling range, e.g., from about 400 F. to about 435 F., and the naphthalene is recovered therefrom in pure form by low temperature crystallization. However, the relatively low napthalene content of such a wide boiling range fraction necessitates the processing of a relatively large volume of material and consequently requires the provision of very extensive chilling and crystallization facilities and the cost of refrigerating a large volume of material other than the desired napthalene. According to a second mode of operation, the naphthalene fraction is taken over a very narrow boiling range, eg., 420-427 F., and as such is of sufficient purity to meet many requirements, e.g., conversion into phthalic anhydride. However, when following such mode of operation an appreciable amount of the naphthalene is lost to the gasoline fraction. This occurs by reason of the fact that part of the naphthalene present in the reactor effluent distills over at temperatures below about 420 F. in the form of low boiling azeotropes with other components ofthe eiiiuent. A portion of the na-phthalene is also )lost to the heavy fraction boiling above about 430 F., but since such fraction is recycled to the reaction zone, the naphthalene contained therein is eventually recovered in substantially pure form.

The present invention is directed to an improved method for carrying out the second of the above-described procedures, and has for its principal object the recovery of the naphthalene which is ordinarily lost to the gasoline fraction in the form of low-boiling azetropes. A more general object is to provide an improved method for producing naphthalene by the dealkylation of alkylnaphthalene-containing hydrocarbon mixtures of petroleum origin, and in particular to provide a means for recovering substantially all of the naphthalene present in the dealkylation reactor etiiuent. Other objects of the the manufacture of phthalic acid. The third of said Patented July 6, 1965 invention will be apparent to those skilled in the art as the description thereof proceeds.

In accordance with the foregoing objects, the process ofthe present invention consists in the catalytic or thermal dealkylation of a suitable alkylnaphthalene-containing feedstock, after which the dealkylation reactor eluent is first treated to remove normally gaseous constituents, and the remaining liquid portion is fractionated to obtain: (l) a gasoline fraction containing light non-naphthalenic materials plus the na-phthalene which is associated therewith in the form of low-boiling azeotropes, (2) a naphthalene fraction containing at least about 95 weight percent of naphthalene, and (3) a heavy fraction comprising a small amount/of naphthalene, unconverted alkylnaphthalenes, and other materials boiling above naphthalene. The rst of `said fractions is passed in Whole or in part to a low temperature crystallization zone wherein the naphthalene contained in said rst fraction is recovered in highly purified4 form. The second of said fractions is taken as a naphthalene product suitable for direct use in fractions is treated to remove heavy ends, and the remainder is returned to the reactor for dealkylation of the unconverted alkylnaphthalenes. Such process is based on my discovery that the non-naphthalenic materials which form low-boiling azeotropes with naphthalene do not co-crystallize or form eutectic solids therewith, so that substantially all of the naphthalene which has heretofore been lost to the light gasoline product in the form of azeotropes can be recovered in a highly pure form, e.g., having a melting point of 79.5 C. or better, by subjecting a fraction containing said azeotropcs to low temperature crystallization.

In the drawings which form a part of this application, FGURE l thereof takes the form of a flow sheet illustrating one way in which the principle of the invention has been applied to a typical catalytic hydrodealkylation process, and FIGURE 2 illustrates in flowsheet form an alternative mode of operation as applied to a thermal dealkylation process. In the interests of simplification, such conventional process Vequipment as pumps, heat exchangers, reboilers, condensers, reflux lines, phase separators, valves, instrumentation, etc., have been omitted from the drawings. n

Referring'now to FIGURE 1, the major items of processing equipment include reactor feed `column 12, catalytic reactor 14, high pressure gas separator 16, llow pressure gas separator 18, gasoline column 20, naphthalene column 22, and a crystallizer-centrifuge combination 24. Light gasoline column 25 is provided to accommodate an optional type of operation, the nature of which is more fully described hereinafter.

The fresh feed, which is suitably an essentially naphthalene-free heavy reformate fraction boiling between about 435 F. and about 735 F. and containing alkylnaphthalenes and non-naphthalenic materials of the same boiling range, is introduced into the system via feed line 25 and is therein joined by a recycle stream flowing in recycle line 28 and containing unconverted alkylnaphthalenes from a previous cycle of operation. The mixture of fresh feed and recycled material passes from line Zoginto feed column 12 Vwhich suitably takes the form of a 20-tray bubble cap column operated to produce an overhead fraction boiling between about 435 F. and about 520 F. and a higher boiling bottoms fraction which is withdrawn via line 30 and passed to storage for use as fuel oil or the like.

The overhead fraction from feed column 12 is passed via line 32 into reactor feed manifold 34 wherein it is joined by a mixture of water vapor and a hydrogencontaining recycle gas stream flowing in line 33. Makeup hydrogen and water are introduced into line 38 from s o lines 40. and 42, respectively. The reactor feed mixture, comprising the hydrocarbons taken overhead from column l2, hydrogen and water, is passed to reactor feed heaterV 44 wherein it is heated toV an incipient reaction tempera-A ture, and the heated mixture is passedV via line 4dto catalytic reactor 14 at such rate that the .space velocity with the reactor ris about'0.4 lvolume of hydrocarbon per hour per volume of catalyst. ,About 81,00 s.c.f. of

oxide, about 9.0 weight percent of molybdenum oxide, and about 2.2 weightpercent of sodium oxide. The reaction Zone is maintained at a temperature of `about 1l00 F. and a pressure of about 1000 p.s.i.g., and Ia substantially uniform temperature proiilewithin the catalyst bed is maintained by introducing a quench Vgas consisting of a part of the hydrogen-containing recycle gas tiowing in line 33 into the reaction Zone at afplurality of points along the length thereof via lines 47. About 1430 s.c.f. of the quench gas are Yemployed per, barrel of hydrocarbon in the reactor feed. i Y

The reactor eluent passes from reactor 14 through eflluent cooler 28 wherein it is cooledto about 160 F., and thence into high pressure separator 16 which Vis operated at a pressure only slightly below that of reactor i4. Within separator 16 the cooled effluent separates into a gaseous phase, a liquid hydrocarbon phase and an aqueous phase. Thel latter is withdrawn via line 50 and is either discarded or recycled-.back to the reactor feed and a relatively small amount of normally gaseous hydrocarbons, is Withdrawn from separator 16 and passed to line 38 for use as the reactor quench gas and for recycle.

to the reactorfeedpmanifold. The liquid hydrocarbon phase in separator 16 is withdrawn via line 52 and is passed through pressure relief valve 54.into low pressure separator 18 which is operated at or near atmospheric with naphthalene.

. manifold. The gaseous phase, which comprises hydrogenv Y' pressure.V Within separator 18 the dissolved normally"- gaseous` hydrocarbons ash olf to formV a gaseous phase which is withdrawn and passed via line 56 to storage for which forms in separator 18 column 20 via rline 58. f

Column Ztl is operated to produce in line 60 an overis passed to light gasoline head fraction comprising light non-naphthalenic materials fraction from column 20 isr passed via transfer line 62 toY naphthalene column 22V which is operated to produce in line 64 an overhead fraction constituting a naphthalene product of about 98.5 percent purity having a melting point of about 78.5 C. Typically,'column 22 is operated use as fuelV gas or the like. The :liquid hydrocarbon phase I at a cut point of yabout 425 F., so thatthe naphthalene y product inline 64 has a boiling range of about'420425 F. The bottoms fraction from column 22, containing a certain amount of naphthalene, unconverted alkylnaphthalenes, non-naphthalenic hydrocarbons of similar boilthe crystals are washed in the centrifuge with a light hydrocarbon such as pentane, andare then stripped to remove traces of the wash liquid by means not shown. The naphthalene product analyzing 99-l% pure and having a melting point of about C. is passed to storage via line 72, and the mother liquor from the centrifuge is withdrawn through line 74 and is passed to storage for use as a gasoline blending stock or otherwise.

In the event it should be desired to decrease the size of crystallizer-centrifuge 24, light gasoline column 25 is provided to separate the gasoline column overhead into a substantially naphthalene-free overhead Vfraction and a bottoms fraction comprising the low-boiling naphthalene azeotropes. When following such mode of operation, valve 68 is rotated clockwise to send the gasoline overhead to lightgasc-line column 25, and valve 70 is rotated counter-clockwise to Vsend the bottoms from column 25 to crystallizer-centrifuge 24. Column 25 is suitably operated at acut point'of about 400 F., so as to produce inline 'i6 a Substantially naphthalene-free 400 F. Vend-point gasoline, and to pass to the crystallizercentrifuge only that portion of the column Ztl overhead which boils over the range 400 F.-420.F.

g Considering now the process of the invention in somewhat greater detail, it is adapted to the dealky-lation of any pretroleum hydrocarbon mixture containing alkylnaphthalenes and materials which, in 4the dealkylated product, cause the formation of low-boiling azeotropes Catalytically or thermally cracked ycycle oils and heavy reformate fractions are most comymonly employed, with platinum-catalyzed reformate fractions being particularly preferred. A particularly preferred process -feedstockof this type consists of a platinum-catalyzed reformate fraction Yboiling between about 435 F. `and Vabout 675 F. and comprising 40-70 percent alkylnaphthalene's. rA secon-d preferred feedstock consists Iof a thermally or catalytically crackedcycle oil extractfraction obtained, for example, byl subjectingV a TCC or FCC cycle `oil of *suitable boiling range to hydroreining, (i.e., hydrodesulfurization and/ or hydrodenltrogenation) `in the presence ofv a cobalt molybdate catalyst (Unining), yand subjecting the hydroreiined product to ysolvent extraction (e.g., with sulfur dioxide or v a glycol)l to obtain an extract product rich in naphthalene yand naphthalenel precursors. Alternatively, the cycle oil can'first'be solvent extracted and the aromatics-rich extract then hydroreiined to obtain a suitable feedstock.

yWith particularly clean cycle oils (i.e., low sulfur and/ Since the process of the invention is directed to thel recovery in substantially pure form of the naphthalene which heretoforehas .been lost in the form of low-boilting azeotropes, anddsince the non-naphthalenic 'hydrocarbons which formysuch azeotropes with naphthalene occur inthe reactor effluent regardless of whether the dealkylation reaction is effected .catalytically vor thering range and high boiling polymers and the like is passed Y via line 66 to recycle line'28 for return to reactor feed column12. y

The gasoline fraction produced in line 60 is passed through three-Way control valvesV 63 and '70to crystallizer-centrifuge 24. The crystallizer section of the latter takes the form of a conventional scraped surface chiller wherein the feed stream is cooled to al temperature of about 10 F. overa period of about 45 minutes to effect crystallization of the naphthalene. From the cry'stallizer section the-slurry of naphthalene crystals in mother liquidv is Vpassed directly to 'the centrifuge sectionwherein the crystals are separated from the mother liquor. Suitably,

mally, the advantages of the process lare attained with both types of operation. When carried out catalytically, the lreaction is usual-ly effected inthe presence of hydrogen, andAv the catalyst. usually'comprises an oxide or sulfide :ofv one or more ofthe metals of groups VIB and VIII of thev periodic system supported on an adsorbent carrier. Suitable active components include the -oxides and/or su-ldes of tungsten, molybdenum, chromium, iron,=cobalt, nickel, .and mixtures thereof. These active Vcomponents Vare supported in minor amounts (e.g.,l 1-20 tively high cracking activity are preferably deactivated by 4including minor amounts of alkalizing components, eg., sodium oxide, in the catalyst composition. The catalyst may be maintained in the form of a -xed bed, Ia compact lmoving bed, or a iluidized bed. Typical catalytic dealkylation conditions include a reaction temperature between about 900 F. and about 1250 F., preferably betweenV about 950 F. and about 1150 F., Ia reaction pressure between about 700 and about 1600 p.s.i.g., and a liquid hourly space velocity of between about 0.2 and about 5 volumes of hydrocarbon per hour per volume of catalyst. When the reaction .is carried out in the presence of hydrogen, as is usually the case, between .about 3000 and about 15,000 s.c.f. of hydrogen (usually in the form of a recycle gas containing 70-95 volume percent of hydrogen) are provided per barrel of hydrocarbon. The use of water vapor to moderate the reaction in accordance with t-he teachings of Doumani, U.S. Patent No. 2,734,929, is a valuable expedient, with the water vapor being provided in an amount representing between about 0.04 and about 0.15 barrel of liquid water per barrel of hydrocarbon. When employing a fixed bed catalyst, it is also desirable to maintain the temperature gradient within the bed at a value below labout 100 F. by introducing a hydrogen-contain- .ing quench gas into the reaction zone at a plurality of points along the length thereof as described previously in connection with FIGURE 1.

Typical thermal dealkylation conditions include a reaction temperature between about 1000 F. and about 1500 F., preferably between about 1100 F. and about 1250 F., a reaction pressure between -about 200 and yabout 1000 4p.s.i.g., and a reaction time `of `between about 2 and about 20 seconds. Conventionally, thermal dealkylation is likewise carried out in the presence of hydrogen, with between about 2000 and about 10,000 s.c.f. of hydrogen being provided per barrel yof hydrocarbon. It is also conventional to effect thermal dealkylationfwithin a fixed, compact moving, or liuidized bed of a non-catalytic inert material, such as sand, pebbles, Alundum chips, and the like.

In general, then, the dealkylation reaction may be carried out under any of the wide variety of conditions known to effect the dealkylation of alkyl-substituted hydrocarbons such as alkylnaphthalenes.

The eliluent which is Withdrawn from the reaction zone is initially treated to separate gaseous from liquid constituents, eg., by condensation. When hydrogen is employed in the reaction zone it is preferably recovered 4as a separate gaseous stream for recycle purposes by initially condensing the reactor effluent at an elevated pressure, `after which the normally gaseous Ihydrocarbons (which for the most part have remained dissolved in the liquid hydrocarbon components) are ashed off by reducing the pressure to a substantially lower value, eg., atmospheric pressure. The remaining liquid components of 4the reactor etiiuent are then passed to the fractionation and crystallization operations which constitute the heart of the invention.

As previously stated, the fractionation operation is carried `out to effect the isolation of lthe following fractions enumerated in order of increasing boiling range: (1) `a ygasoline fraction containing non-naphthalenic components and substantially all of the napht-halene which distills in the form of low-'boiling azeotropes, (2) a naphthaleneproduct fraction which contains at least about' 95 weight percent of naphthalene, (3) aheavy fraction which contains unconverted alkylnaphthalenes and non-naphthalenic hydrocarbons of similarfboiling range, and which is recycled to the dealkylation zone, and (4) a high-boiling fraction which comprises polymeric materials and the like 'and `which is `taken as a process product useful as fuel oil or the like.

It will be apparent that while certain of the cut points between these respective fractions are more critical than others, a certain degree of latitude is permitted depending on the desired purity of the naphthalene fraction and the extent to which it is desired to recover the naphthalene which occurs in the form of low-boiling azeotropes. Also, the cut points will vary somewhat with the various process parameters. Thus, in FIGURE 1 the cut point at which gasoline column 20 is operated to produce the first of the fractions identified above will vdepend upon the boiling points of the naphthalene-conhand, a more highly purified second fraction may be obtained (at the expense of losing some of the nonazeotroped naphthalene to the first fraction) by setting the cut point somewhat higher, e.g., at about 420 F. or even slightly higher. Thus, in FIGURE 1, column 20 is usually operated to produce an overhead fraction having a maximum true boiling point between about 415 F. and about 420 F.

The cut point between the second and third of the above-identiedl fractions is likewise governed by the desired naphthalene content of the second fraction. By setting the cut point at a relatively low value, e.g., at about 425 F., a high concentration of naphthalene is obtained in the second fraction at the expense of losing some naphthalene to the third fraction (which naphthalene, however, is eventually recovered), whereas by setting such cut point at a relatively high value, eg., at about 435 F., a somewhat less concentrated naphthalene product fraction is obtained. Thus, in FIGURE 1, column 22 is operated to produce an overhead frac-l tion having a maximum true boiling point between about 425 F. and about 435 F., preferably between about 425 F. and about 430 F.

The cut point between the third and fourth of the above-identified fractions is least critical of all, and is governed primarily by the nature of the dealkylation step and the feedstock employed. Desirably, such cut point is selected to separate materials capable of further dealkylation from materials which undergo no useful reaction in the dealkylation zone. Usually, the latter materials boil above about 485 F., so that, in FIGURE 1, column 12 is operated to produce an overhead fraction having a maximum true boiling point of at least about 485 F. but not greater than about 550 F., preferably about 510 F.

As has been previously described, the first of the fractions identied above may be further fractionated to produce a low-boiling overhead fraction which is substantially naphthalene-free (e.g., containing less than about 1 weight percent of naphthalene) and a bottoms fraction which contains naphthalene associated with nonnaphthalenic materials in the form of low-boiling azeotropes. vWhen following such mode of procedure optimum operation is usually attained when this fraction is carried out to produce an overhead fraction having a maximum true boiling point between about 395 F. and about 405 F., usually about 400 F.

Selection of the two alternative ways for handling the iirst of the above-identified essential fractions (i.e., passing the entire fraction to the crystallization operation versus further fractionation to separate a substantially naphthalene-free fraction and passing the remainder to the crystallization operation) is primarily a matter of economics. Since the lirst mode of operation requires handling a larger volume of material in the crystallization operation, more extensive crystallization facilities and higher refrigeration costs are involved. On the other hand, While the second mode of operation perf effect separation fof normally gaseous components.

mits a reduction in theseitems, an additionaldistillation column is required.

. The crystallization step is carried out in the conventional manner, i.e., by cooling'the feed stream to a relatively low temperature to obtain a slurry of naphthalene o f a jacketed conduit'through which the feed stream is passed.V Scrapers adapted to be rotated against thewalls of the conduit are provided to prevent crystalline mate-V rial from building up on the walls of the conduit and interfering with the transfer of heat therethrough. Conventionally, the jacket is divided into two or more sections through which different refrigerants are circulated at sucessively lowertemperatures. The temperature to which the crytsallizer feed stream is cooled and the rate at which such cooling is effected depend on the desired purity of the product and the means and vconditions employed for separating the crystals from the mother liquor.

In the practice of the present invention lhave found it. sattisfactory to chill the feed to Va temperature between' about F. and about 0F., preferably between "about 15 F. and about 5 F., over a period of -60 minutes when employing a centrifuge for separating the crystals from the'mother liquor. Usually it is desirable to wash the crystals with a light hydrocarbon wash liquid, eg., pentane, light gasoline, etc., and to remove traces of the wash liquid by steam stripping, distillation, etc. lf necessary, the naphthalene product may be treated with clay or acidic salts in the known manner to remove Ycolor bodies. The mother liquor recovered suitable for recycling'to reactor feed manifold 100. I The liquid portion of the reactor etiluent is withdrawn from separator 124 and is passed via transfer line 128 to gasoline column 130.

Gasoline column 130 is operated to produce in line 132 an overhead fraction having a Vmaximum boiling point of about 420 F. Said fraction is introduced from line 132 into light gasoline column 134 which is operated to produce in line 136V an overhead fraction of substantially Y naphthalene-fi'ee light gasoline having a maximum boiling point of about 400 F. rl`he bottoms fraction from co1- umn 130 is passed via line 138 to naphthalene column-140 which is'operated to produce in product'line 142 an overhead fraction boiling between about 420 F. and about 427 F. and containing about 98.6 Weightpercent naphthalene. The bottoms fraction from column 140, comprising unconverted alkylnaphthalenes and other componentsfof the reactorreflluent boiling above about 427 F., is passed to recycle line 102 for return to feed column 104 and further dealkylation.

The bottoms fraction from column 134, comprising azeotroped naphthalene and non-naphthalenic materials boiling between about 400 F. 'and about l420 F., is

v passed via line 144 (to chillerl 146. The latter is of the from the crystallization operation is suitable for use as a Y gasoline blending stock. In general, then, Yin eifecting the crystallization step any of the techniques and equipment customarily employed in such type of operation may be employed, and any of theV known treatmentsfor the purication of Ypetroleum or coal tar naphthalene may be applied in the practice of the' present process.`

Referring now to FGURE 2, the process therebyillustratedemploys thermal-dealkylation and an alternative fractionation scheme. The feedstock, which consists of a platinum-catalyzed reformate fraction boiling over the range 475-570F. and containing about 43.7 Weight percent of mono-met-hylnaphthalene, about 33.0 weight percent of higher,alkylnaphthalenes, with the remainder being non-naphthalenic hydrocarbons, is introduced into the process system via line 100 and is therein joined by the liquid portion of the reactor .eiliuent flowing in line 102. The mixture is introduced into feed column 104 which is operated to produce in line 106 an overhead fraction having a maximum boiling point of labout 510 F. Said-fraction is introduced from line 106 into reactor feed manifold 103 and the bottoms fraction'is passed to storage via line 112. L

Thereactor feed mixture kowing in manifold 108 ris admixed with about 5000 scf/bbl. of hydrogen introduced into the system from line 110, and passes .Y through feed preheater 114 which is operated topreheat, the reactor feed to about 900 F. The heated feed then passes through line 116 to reactor 118 within which the dealkylation is effected. Reactor 118 consists of a fire- .brick lined shell iilled with Z-inch Alundum balls, and is maintained at a temperature of about 13.25 F. and a conventional Vscrapedsurface type, the vjacket rof which 'is divided into three sections 14de-145e to provide for the use of three different refrigerants at successively lower temperatures; VColdY (50 F.) water is circulated through section 146g, chilled (--8KF.)v methanoly through section y146b, and cold (-40" F.) methanol through section 146C. The residence time of the feed within the Chiller is about 45 minutes, and the temperature of the slurry which is Withdrawn from the downstream end through line 148 is about 10 F. From line 14S, the slurry passes to centrifuge 150 wherein the crystals are separated from the mother liquor. Within the centrifuge the crystals are washed with a stream of cold pentane introducedY from line 152, and the washed crystals are withdrawn through line 154 Vand passed to heater 156. Within the latter ythe naphthalene crystals are melted, and the molten naphthaleneris passed to a small stripping column 15?` which is operated to produce inline 160 the pentane adhering .to the crystals taken'fromthe centrifuge. The bottoms product from stripper 150, constituting substantially purel (99.9%) naphthalene, is passed to storage through'product line 162. The mother liquorVis withdrawn from the centrifuge via line 164, and is passed to stripper 166 which is operated to produce the pentane wash liquid in overhead line 16S and pentane-free mother liquorrin Vline 170. The recovered penta'ne flowing in lines 160 and 168 is returned to line 152 for re-introduction into'centrifuge 150. Make-up pentaue may be added as needed from line 172.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the methods or materials employed provided the step or steps stated byy any of the following claims, or the equivalent of such stated step or steps, be employed. i y

I, therefore, particularly point out and distinctly claim as myinvention:` t t 1. In a process wherein an alkylnaphthalene-containy ing petroleum hydrocarbon feedstock boiling above about 430 F. Yand selected fromthe class consisting of catalyt-icreformates, -catalytically cracked cycle `oils and thermally cracked cycle oils is passed, together with added hydrogen, through a dealkyl'ation zone maintained at an elevated temperature and anelevated pressure suliicient to effect dealkylation of a substantial amount of said alkylnaphthalene, wherebythereis obtained a dealkylation zone effluent `comprising naphthalene andnon-naphthalenic hydrocarbonswhich form low-boilingazeotropes with naphthalene, the improvement which comprises fractionating said effluent to obtain a first fraction containing atleast about V weight percent of naphthalene, a second fraction having a boiling range below that of said first fraction and comprising azeotroped naphthalene, and a third fraction having a boiling range above that of said first fraction and comprising alkylnaphthalenes; returning an alkylnapthalene-containing portion of said third fraction to said dealkylation zone; cooling a naphthalene-containing portion of said second fraction in a crystallization zone to effect the formation of crystalline naphthalene; and separating said crystalline naphthalene from the mother liquor.

2. A process as defined by claim 1 wherein substantially all of said second fraction is cooled in said crystallization zone.

3. A process as defined by claim 1 wherein said second fraction is further fractionated to obtain a low-boiling substantially naphthalene-free portion and a higher boiling portion comprising azeotroped naphthalene; and said higher boiling portion is cooled in said crystallization zone.

4. A process as deiined by claim 1 wherein said dealkylation zone contains a catalyst comprising a mixture of the oxides of molybdenum and cobalt supported on an alumina base, and is maintained at a temperature between about 900 F. and about 1250 F. and a pressure between about 700 p.s.i.g. and about 1600 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 3000 s.c.f and about 15,000 s.c.f. per barrel. of hydrocarbon introduced into said zone.

5. A process as defined by claim 1 wherein said dealkylation zone contains a non-catalytic solid material, and is maintained at a temperature between about 1000 F. and about 1500 F. and at a pressure between about 200 p.s.i.g. and about 1100 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 2000 s.c.f. and about 10,000 s.c.f. per barrel of hydrocarbon introduced into said zone.

6. The process for obtaining naphthalene which comprises (1) forming a feed mixture comprising the hereinafter identified recycle stream, fresh petroleum hydrocarbon feedstock boiling above about 430 F. and containing a substantial amount of alkylnaphthalenes, and hydrogen, said feedstock being selected from the class consisting of catalytic reformate, catalytically cracked cycle oils, and thermally cracked cycle oils; (2) passing said feed mixture into a dealkylation zone maintained under conditions of elevated temperature and elevated pressure suicient to effect the dealkylation of a substantial amount of said alkylnaphthalenes; (3) withdrawing a dealkylated eluent from said dealkylation zone and condensing said effluent to obtain a liquid effluent phase and a gaseous effluent phase; (4) distilling said liquid effluent phase to obtain a first fraction boiling between about 420 F. and about 430 F. and containing at least about 95 weight percent of naphthalene, a second fraction having a boiling range below that of said first fraction, and a third fraction having a boiling range above that of said first fraction; (5) returning an alkylnaphthalene-containing portion of said third fraction to the aforesaid step (1) as said recycle stream; (6) introducing a naphthalene-containing portion of said second fraction into a crystallization zone maintained at a low temperature suiiicient to effect crystallization of a substantial amount of the naphthalene introduced therein; and (7) separating the crystalline naphthalene so formed from the mother liquor.

7. A process as dened by claim 6 wherein, in step (6), substantially all of said second fraction is introduced into said crystallization zone as said naphthalene-containing portion of said second fraction.

8. A process as defined by claim 6 wherein said second fraction is further fractionated to obtain a low-boiling substantially naphthalene-free portion and a higher boiling portion containing azeotroped naphthalene; and said higher boiling portion is introduced into said crystallization zone as said naphthalene-containing portion of said second fraction.

9. A process as defined by claim 6 wherein said dealkylation zone contains a catalyst comprising a mixture of the oxides of molybdenum and cobalt supported on an alumina base, and is maintained at a temperature between about 900 F. and about 1250 F., and at a pressure between about 700 p.s.i.g. and about 1600 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 3000 s.c.f. and about 15,000 s.c.f. per barrel of hydrocarbon introduced into said zone.

10. A process as defined by claim 6 wherein said dealkylation zone contains a non-catalytic solid material, and is maintained at a tmeperature between about 1000 F. and about 1500 F. and at a pressure between about 200 p.s.i.g. and about 1100 p.s.i.g., and hydrogen is introduced into said dealkylation zone in an amount representing between about 2000 s.c.f. and about 10,000 s.c.f. per barrel of hydrocarbon introduced into said zone.

11. The process for obtaining naphthalene which comprises (l) forming a feed mixture comprising the hereinafter identified recycle stream, a platinum-catalyzed petroleum hydrocarbon reformate fraction boiling above about 430 F. and containing a substantial amount of alkylnaphthalenes, and between about 3000 and about 15,000 s,c.f. of hydrogen per barrel of hydrocarbon; (2) contacting said feed mixture with a fixed bed of a dealkylation catalyst comprising a mixture of the oxides of molybdenum and cobalt supported on silica-stabilized alumina containing a minor amount of an alkali, said contacting being effected at a liquid hourly space velocity of between about 0.2 and about 5 volumes of hydrocarbon per hour per volume of catalyst and at a temperature between about 900 F. and about 1250 F. and a pressure between about 700 and about 1600 p.s.i.g.; (3) withdrawing a dealkylated etlluent from said dealkylation zone and fractionating it to obtain: (rz) a normally gaseous fraction, (b) a substantially naphthalene-free light gasoline fraction having a maximum boiling point of about 405 F., (c) a higher boiling naphthalene-containing rst intermediate fraction having a maximum boiling point of about 420 F., (d) a naphthalene fraction containing at least about weight percent naphthalene, (e) a higher boiling second intermediate fraction having a maximum boiling point of about 550 F., and (f) a higher boiling bottoms fraction; (4) returning said second intermediate fraction to the aforesaid step (1) as said recycle stream; (5) cooling said rst intermediate fraction to a temperature between 20 F. and about 0 F. to effect crystallization of the naphthalene contained therein; and (6) separating the crystalline naphthalene so formed from the mother liquor.

12. A process as defined by claim 11 wherein said catalyst comprises a silica-stabilized alumina base having distended thereon about 3 weight percent of cobalt oxide, about 9 weight percent of molybdenum oxide, and about 2.2 weight percent of sodium oxide, said feed mixture contains water vapor in an amount corresponding to between about 0.04 and about 0.15 barrel of liquid water per barrel of hydrocarbon, and hydrogen is introduced into said catalyst bed at a plurality of points along the length thereof and in an amount suicient to maintain tlle0 temperature gradient therein at a value below about References Cited bythe Examiner UNITED STATES PATENTS 2,336,244 12/43 Happel 260--674 2,674,635 4/54 Beckberger 260-672 2,694,095 11/ 54 Medcalf et al 260-672 2,858,348 10/58 Bosmajian et al 260--674 ALPHONSO D. SULLIVAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,193,593 July 6, 1965 Oscar C. Eubank fied that error appears n the above numbered pat- It is hereby certi on and that the said Letters Patent should read as ent requiring correcti corrected below.

Column l0, line 15, for "tm'efperature" read temperature line 50, for "between 20 13.," read between about -20 F s Signed and sealed this 28th day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER Attestng Officer EDWARD J. BRENNER Commissioner of Patents 

1. IN A PROCESS WHEREIN AN ALKYLNAPHTHALENE-CONTAINING PETROLEUM HYDROCARBON FEEDSTOCK BOILING ABOVE ABOUT 430*F. AND SELECTED FROM THE CLASS CONSISTING OF CATALYTIC REFORMATES, CATALYTICALLY CRACKED CYCLE OILS AND THERMALLY CRACKED CYCLE OILS IS PASSED, TOGETHER WITH ADDED HYDROGEN, THROUGH A DEALKYLATION ZONE MAINTAINED AT AN ELEVATED TEMPERATURE AND AN ELEVATED PRESSURE SUFFICIENT TO EFFECT DEALKYLATION OF A SUBSTANTIAL AMOUNT OF SAID ALKYLNAPHTHALENE, WHEREBY THERE IS OBTAINED A DEALKYLATION ZONE EFFLUENT COMPRISING NAPHTHALENE AND NON-NAPHTHALENIC HYDROCARBON WHICH FORM LOW-BOILING AZETROPES WITH NAPHTHALENE, THE IMPROVEMENT WHICH COMPRISES FRACTIONATING SAID EFFLUENT TO OBTAIN A FIRST FRACTION CONTAINING AT LEAST ABOUT 95 WEIGHT PERCENT OF NAPHTHALENE, A SECOND FRACTION HAVING A BOILING RANGE BELOW THAT OF SAID FIRST FRACTION AND COMPRISING AZETROPED NAPHTHALENE, AND A THIRD FRACTION HAVING A BOILING RANGE ABOVE THAT OF SAID FIRST FRACTION AND COMPRISING ALKYLNAPHTHALENES; RETURNING AN ALKYL 